Did many families in hiding get discovered due to children not being able to be silent? I refer to those like the franks hidden in secret lofts rooms and cellars.
A bit morbid I know but playing hide and seek with my young lad made me think, in WW2 when the nazis were actively hunting Jewish and minority families, were any that were in hiding spots such as false floors and attics discovered because younger members gave them away?
There are no data on how many families this happened to.
However, we have to take two things into account that would lead us to answer: probably very few.
First, most Jewish people were not in hiding, they were deceived into reporting for "deportation to work in the East" (for those living in Western and Southern Europe), or were simply rounded up in razzias and raids, or herded into ghettos at first, from which there was virtually no escaping later (for those living in Eastern Europe), or simply marched off to be shot when the German army overran their towns (for those in the Soviet Union).
Those who succeeded in seeing through the deception or managed to escape from a ghetto and went into hiding almost never took their smaller children into hiding with them. And this for precisely the reason you mention: you can't keep a young child quiet for months or years. It just isn't feasible. Children were therefore almost invariably sent away to hide out in the open, either with willing (or richly paid - or both) gentile families, posing as a distant family member, or child of a friend, or in orphanages, boarding schools and similar institutions, with the connivance of the staff, but not of the other children.
In two relatively recent studies of "hidden" Jewish children in Belgium, Nele De Clercq's 2006 Master thesis Verborgen Kinderen and Suzanne Vromen's Hidden Children of the Holocaust, Oxford University Press, 2008, none of the former hidden children interviewed had been in hiding with their parents. They were invariably placed with Gentiles.